1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and, more particularly relates to a semiconductor device having insulating films formed by using polysilazane and a manufacturing method of the semiconductor device.
2. Description of Related Art
Conventionally, in manufacturing process of a semiconductor device, insulating films in narrow regions such as an STI (Shallow Trench Isolation) trench and a space between gate electrodes or bit lines are formed by means of a HDP-CVD (High Density Plasma-Chemical Vapor Deposition) method, depositing BPSG (Boron Phosphorus Silicon Glass) and reflowing the deposited BPSG, or the like. With downsizing of elements, however, the STI trenches or the spaces between gate electrodes or bit lines have become narrower and accordingly it has become difficult to form the insulating films in these regions by the method mentioned above.
FIG. 39 is a schematic cross-sectional view showing an example in which a silicon dioxide film is formed between bit lines by the HDP-CVD method. As shown in FIG. 39, cell contacts 502 are formed in a first interlayer insulating film 501, and a second interlayer insulating film 504 and bit contacts 505 are formed thereon. Bit lines 506 are formed on the bit contacts 505, and a cap insulating film 507 and a side-wall insulating film 508 are formed on upper and side surfaces of each of the bit lines 506, respectively. A metal silicide film 503 is formed on an upper surface of each of the cell contacts 502 to reduce contact resistance between the cell contact 502 and the adjacent bit contact 505. A silicon dioxide film 509 is formed by the HDP-CVD method to fill spaces between the bit lines 506. However, voids 510 are adversely produced in the narrow spaces between the bit lines 506.
Consequently, there has been a need to use polysilazane with a satisfactory filling capability to form a silicon dioxide film in such narrow regions (see, for example, Japanese Patent Application Laid-open Nos. 2005-347636 and 2004-179614).
To form a silicon dioxide film by using polysilazane, it is necessary to apply a polysilazane solution by spin coating, perform annealing (steaming) in a steam (H2O) atmosphere, and then reform the polysilazane into a silicon dioxide film with a high density. This is for a following reason. Because the polysilazane includes a composition of “—SiH2NH—”, coating of the polysilazane solution and subsequent heat treatment in a nonoxidizing atmosphere such as nitrogen atmosphere produces a silicon nitride film. The silicon nitride film, however, has a great stress and is improper to be used as an interlayer insulating film. Therefore, it is necessary to perform the annealing in the steam atmosphere (oxidizing atmosphere) after coating of the polysilazane, thereby removing N in the coated film and reforming the film into a silicon dioxide film. However, the steaming may oxidize a metal film, a polycrystalline silicon film, or a silicon substrate in lower layers. For example, when the silicon dioxide film in the semiconductor device having the structure shown in FIG. 39 is formed by using the polysilazane instead of by the HDP-CVD method, the metal silicide film 503 is oxidized and resistance is increased. Therefore, an oxidation-resistant liner film needs to be formed before coating of the polysilazane.
FIG. 40 shows an example in which a silicon nitride film is used as an oxidation-resistant liner film and a silicon dioxide film is made of polysilazane. In FIG. 40, constituent elements identical to those in FIG. 39 are denoted by like reference numerals and explanations thereof are omitted. As shown in FIG. 40, a silicon nitride film 601 is continuously formed on surfaces of the cap insulating film 507 and the side-wall insulating film 508 covering the bit lines 506, and on parts of an upper surface of the second interlayer insulating film 504 exposed between the bit lines 506. Polysilazane is coated thereon and then annealing is performed in a steam atmosphere, thereby forming a silicon dioxide film 602.
However, it has been found that the polysilazane in narrow groove-like regions 603 (see FIG. 40) between the bit lines 506 is not adequately reformed by the steaming when the silicon nitride film is used as the liner film 601 for the polysilazane.
FIG. 41 shows the semiconductor device shown in FIG. 40 after being steamed, then cut in section as shown, and treated with a hydrofluoric acid. As shown in FIG. 41, the polysilazane above the cap insulating film 507 is adequately reformed into a dense silicon dioxide film, and therefore remains hardly etched in the treatment with the hydrofluoric acid. On the other hand, a plurality of voids 604 is formed in the groove-like regions 603 between the bit lines 506. That is, the polysilazane in the regions 603 is not adequately reformed into a dense silicon dioxide film, and there remain parts having quite high etching rates in the treatment with the hydrofluoric acid than in the other parts adequately reformed, which are etched to form the voids 604.
It is considered that a reason why the polysilazane is adequately reformed is that outgassing of ammonia (NH3) from a surface of the silicon nitride film 601 as the liner film occurs during the steaming, which prevents Si—N bonds in the polysilazane from being substituted for Si—O bonds.
When the silicon dioxide film inadequately reformed is used as an interlayer insulating film, the interlayer insulating film is etched horizontally, that is, so as to form the voids 604 as shown in FIG. 41, during etching of the interlayer insulating film for contact hole formation, for example. When a plug material is subsequently formed in the contact holes, the plug material is filled also in the voids and adjacent contact plugs are short-circuited.
The conventional problems have been explained using the example in which the polysilazane is used to fill a silicon dioxide film between bit lines of a DRAM (Dynamic Random Access Memory). These problems can also occur in narrow regions between gate electrodes, STI regions, and the like.